Thermal inkjet (TIJ) printers are now commonly found in homes and offices. TIJ printers offer good print quality at a very affordable price. TIJ printers employ pens to apply ink to paper or other printing medium. For example, a black pen is provided for printing black ink. Similarly, a multi-color pen is utilized to apply color inks to a paper. Each pen typically includes a cavity for holding the ink and a nib for delivering the ink. The nib holds a print head, which is typically made of a silicon material that controls the delivery of the ink. The print head includes hundreds of orifices through which ink is delivered.
Some orifices are fired very frequently. Other orifices are fired very infrequently. In any case, inkjet pens require frequent wiping to remove excess ink from the orifices and to prevent ink depositions from hardening in or around the orifices. As can be appreciated, hardened ink deposits can cause the orifices to clog or jam, thereby adversely affecting print quality.
Currently, some thermal inkjet (TIJ) printers include a sub-assembly that is often referred to as a “service station” for maintaining the TIJ pens. The service station maintains the pens by wiping excess ink from the orifice, thereby increasing the life of the pens and enhancing the performance of the pens.
Multi-Pass Printer with Stationary Service Station
FIG. 1 illustrates a first type of prior art multi-pass TIJ printer where the service station is stationary, and the carriage moves with respect to the stationary service station. The multi-pass printer has nozzles that are positioned in a first orientation 110. The first orientation 110 is generally parallel to the direction of carriage motion. The black ink firing nozzles 114 are arranged generally in a single horizontal band. Similarly, the color ink firing nozzles 118 are arranged generally in horizontal bands stack upon each other with each band having nozzles for a particular color (e.g., cyan, magenta and yellow). This type of printer requires multiple passes to complete a printing job.
A piece of paper is fed through a paper path in the printer. A feed roller and other rollers are driven by a plurality of gear trains that are driven by a paper path DC motor. A carriage moves generally in the directions shown and is driven by a carriage DC motor. A linear encoder is also provided for controlling the movement of the carriage. The carriage includes a plurality of pens that deposit ink onto the paper. A stationary service station is provided for maintaining the pens. Maintenance of the pens involves periodically wiping the pens and capping the pens when the pens are not in use.
For these printers, the motion required for wiping and capping the pens is parallel to the direction of the pen movement on the carriage. These TIJ printers (e.g., Lexmark brand TIJ printers) use the motion of the pens across the paper, which is driven by the carriage DC motor, and a stationary service station to service the pens.
At the end of a print job, the pens move to the far right side of the printer, where the pens hit a lever that moves the caps into place. When a new print job starts, the pens are moved to the extreme left of the printer. The start of this movement releases the capping switch and lowers the caps halfway, thereby bringing the wipers into position. As the pens continue their motion, the orifices are wiped. After the final wiping motion is completed, the pen motion pulls the wipers into a “rest” position that does not interfere with the normal operation of the carriage.
One disadvantage of these types of printers is the speed at which pages are printed, which is typically measured by the number of pages per minute. As can be appreciated, multi-pass type printers typically take a longer time to print pages than a single-pass printer that is described in greater detail hereinafter. Consequently, as the demand for printers that have faster printing speeds increases, the demand for single-pass printers increases proportionately.
One benefit of a stationary service station is that the arrangement is relatively cost-effective. Unfortunately, this type of arrangement for pen servicing and maintenance is not suitable for single-pass printers for the reasons set forth hereinafter.
Single-Pass Printer with Moving Service Station
FIG. 2 illustrates a second type of prior art single-pass TIJ printer where a dedicated motor controls the movement of the service station. The single-pass printer (also referred to as a complete swath printer) has nozzles that are positioned in an second orientation 120 that is generally perpendicular to the direction of carriage motion, thereby enabling all the different color nozzles to fire simultaneously. The black ink firing nozzles 124 are arranged generally in a single vertical band. Similarly, the color ink firing nozzles 128 are arranged generally in vertical bands that are arranged adjacent to with each other with each vertical band having nozzles for a particular color (e.g., cyan, magenta and yellow). Examples of this type of TIJ printer include the Hewlett-Packard 800 and 900 series.
For these printers, motion of a service station (e.g., the service station pallet) is required to perform the pen-servicing operations. This motion is achieved by using a stepper motor to maneuver the entire service station assembly.
For multiple colors, the wiping function performed by the service station has an additional complication. This complication is that the service station needs to be moved in a particular manner with respect to the firing nozzles in order to prevent cross-contamination of the ink.
In color printers, if the wiper crosses from cyan to magenta to yellow, the color inks contaminate each other. In other words, when one wiper blade services multiple colors, and a particular portion of the wiper (e.g., a particular wiper surface) is passed over firing nozzles of different colors, the ink supplies are contaminated.
When the wiping motion runs along a single color without crossing different color boundaries (i.e., a particular portion of the wiper passes over firing nozzles of a single color), then the inks do not contaminate each other. Consequently, it is important in the design of the service station that the direction of the wipe is ensured to be along the same direction as the placement of the firing nozzles of the print head.
Additionally, perpendicular TIJ printers provide an isolated space for the spittoon and move that spittoon into position. The isolation keeps the excess ink away from the other contents of the printer.
It is noted that the Hewlett-Packard type of single-pass printers utilize a platform, a separate dedicated motor to drive the platform, and one or more gear trains for transferring the motion of the motor to the platform. These components are needed to cause the wiper blades that are mounted on the platform to perform the maintenance functions of the service station. As can be appreciated, these components increase the weight, cost, and complexity of the printer.
As the costs of printers decreases and the competition in the thermal inkjet printer market increases, there is a constant demand for designs for the various sub-assemblies that can reduce the number of parts needed for a particular sub-assembly and hence reduce the costs associated with manufacturing the printer.
Consequently, it is desirable for there to be a service station that performs the wiping and cleaning functions of prior art service station while at the same time reducing the part count and costs associated with the manufacture of the service station.
Based on the foregoing, there remains a need for pen maintenance method and system for thermal inkjet printers that overcomes the disadvantages set forth previously.